Recent studies have highlighted the significance of Fc-FcR interactions to achieve in vivo protection for neutralizing antibodies to HIV and other viruses or bacterial toxins through mechanisms including ADCC and ADCVl. We have defined both the amino acid and glycan requirements for IgG Fc binding to Fc?Rs and developed animal models based on novel strains of Fc?R humanized mice to determine the impact of amino acid and glycan modifications of human IgGs on their in vivo function. Despite the growing appreciation for the importance of Fc mediated effector functions to the in vivo potency of antibody mediated viral neutralization for bNAbs to HIV, no systematic studies have been performed to determine the optimal Fc structure that will result in these activities. We will characterize the contributions of Fc structure and effector functions to the activities of the bNAbs isolated by Nussenzweig and generate modified bNAbs optimized for Fc effector functions. These re-engineered bNAbs will be tested in vitro for neutralization, ADCC and ADCVBI and, in collaboration with Nussenzweig, in a novel in vivo neutralization assay, based on the TZM-bl assay in mice that carry human Fc?R. In collaboration with Bjorkman we will obtain structural information for these modified antibody Fc's, alone and in complex to specific Fc?Rs, These data will direct the generation of additional variants to further enhance Fc-Fc?R function. These studies will result in the generation of novel, bNAbs optimized for both neutralization and effector function and provide the framework to develop immunization strategies that will result in bNAbs with optimal effector properties.